<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>javascript study</title>
</head>

<body>
    <script>
        function getValue() {
            var a, b, c;
            a = void (b = 5, c = 7);
            document.write('a = ' + a + ' b = ' + b + ' c = ' + c);
        }    
    </script>
    <a href="javascript:void(0)">单击此处什么也不会发生</a>
    <br>
    <!-- 计算一个表达式 -->
    <a href="javascript:void(alert('Warning!!!'))">点我!</a>
    <button onclick="getValue()">测试</button>
</body>

</html>